Pulling Out Feathers: Group Living Stresses Ravens

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As anyone who's watched a reality show knows, group living can
put a strain on relationships. Now, researchers have found living
in a flock stresses out young ravens — an avian anxiety that
resolves only when the birds pair off and gain territory.

A group of ravens is called an "unkindness" or "conspiracy,"
which seems fitting, since ravens are traditionally considered
creepy; in fact, seeing many of them in one place can induce
Hitchcockian "The Birds"-like flashbacks in even the least
ornithophobic
(those people with a fear of birds). But humans aren't the only
animals who show distaste for groups of the jet-black birds. New
research is showing the birds
get stressed out when they find themselves in large groups,
too.

Study author Bernd Heinrich, of the University of Vermont,
describes these groups of young ravens as a "mobile discotheque"
— a group of males fighting for dominance and
females trying to find mates — something reminiscent of the
cast of the MTV reality show "Jersey Shore."

The results suggest life in the fast lane of the ravens' mobile
discotheque is much more stressful than life as a territorial
breeding pair, and it's this stress that might push the ravens to
settle down, said lead researcher Nuria Selva, of the Institute
of Nature Conservation at the Polish Academy of Sciences in
Krako.

"We expected the opposite," Selva told LiveScience. "Living in
groups is full of benefits," including protection from predators,
increased availability of food and freedom to wander from place
to place. When the birds leave their groups, they have to protect
their own territory from other birds, such as raptors and flocks
of young ravens.

Understanding the unkindness

To get a better understanding of the bird's lifestyles, the
researchers collected fecal samples from wild ravens that were
either from young adults living in a flock, or from the territory
of older birds living with a mate. They tested the samples for
the levels of a stress hormone, called corticosterone, which
regulates a bird's use of fuel, its immune health and its stress
response. They also tested the samples to determine the sex of
the animal and if it was infected by parasites.

The flock-living ravens had higher stress levels than those
paired up. "By logic, we would think that to maintain a territory
would be much more stressful," Selva said, because these birds
have to fight for their land. Also, the territory-based females
had much lower hormones than their mates, which the researchers
say might be due to their increased energetic demands on the
males to defend the territory.

While Selva didn't expect these lower levels, Wolfgang Goymann,
of the Max-Plank Institute for Ornithology, who wasn't involved
in the study, says he thinks it makes sense. "They live in a much
more stable and predictable environment than the nonbreeders and
hence I would have expected that their life is less demanding."

The flock is likely a stressful place because of the aggressive
interactions that occur in competition for food and a place on
the dominance hierarchy, he said. In youth, though, the
detrimental effects of the increased stress seem to be worth it
in exchange for the safety in numbers from being in a flock.

Stressful group life

Mareike Stöwe, a researcher at University of Veterinary Medicine,
in Austria notes that stress hormone levels could be influenced
by earlier events experienced by the birds, so it's difficult to
truly know the baseline levels. "We never know what the birds
experienced before showing up at the carcass," Stöwe, who wasn't
involved in the study, told LiveScience in an e-mail. "So it
might well be that the hormone content in the droppings (at least
in some of them) reflects a stress response to previous events
(fights etc.)."

The samples were taken in January and February, a time when the
ravens are pairing up and territories are secured. So those
adult
males without mates likely would be very stressed, Stöwe
said, and it would be interesting to see their stress hormone
levels at other times of the year.

Selva agreed that the higher stress levels may be a response to
the competition occurring in these groups, with the increased
stress hormones triggering a boost of energy use. That fuel boost
would then allow the birds to travel and fight with the group to
gain dominance.

The stress may also nudge young ravens to grow up. "The hormonal
mechanisms play an important role in stepping from the young
adult life to the adult life, we think," Selva said.